Multispectral plasmonic thermal imaging device

ABSTRACT

A computer-eimplemented thermal imaging device having an optically-sensitive layer that includes a superpixel having at least one pixel. The at least one pixel includes a plasmonic absorber configured to obtain radiance measurements of electromagnetic radiation emitted from an object at a plurality of wavelengths. The device further includes a processor configured to determine an emissivity and temperature for the electromagnetic radiation received at the plasmonic material from the object using the radiance measurements and to form an image of the object from the determined emissivity and temperature.

DOMESTIC PRIORITY

This application is a divisional of U.S. patent application Ser. No.15/802,836, filed Nov. 3, 2017, the disclosure of which is incorporatedby reference herein in its entirety.

BACKGROUND

The present invention relates to thermal imaging devices, and morespecifically, to a thermal imaging device using plasmonic materials.

Thermographic cameras produce thermal images of objects in their fieldof view based on the temperature of the objects. Objects continuouslyemit electromagnetic radiation. The spectrum and intensity of theemitted electromagnetic radiation is a function of the temperature ofthe object. For an ideal, perfectly absorbing object (i.e., a“blackbody”), the emitted spectrum is described by Planck's law. Formost objects however this spectrum flux is modified by the object'semissivity.

SUMMARY

Embodiments of the present invention are directed to a thermal imagingdevice including: an optically-sensitive layer including a superpixelhaving at least one pixel, the at least one pixel including a plasmonicabsorber configured to obtain radiance measurements of electromagneticradiation emitted from an object at a plurality of wavelengths; and aprocessor configured to determine an emissivity and temperature for theelectromagnetic radiation received at the plasmonic material from theobject using the radiance measurements and to form an image of theobject from the determined emissivity and temperature.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a thermographic camera system according to embodiments ofthe present invention;

FIG. 2 shows a focal plane array that is included in the thermographiccamera according to embodiments of the present invention in order tocreate a thermal image;

FIG. 3 shows a detailed view of an exemplary superpixel of the focalplane array of FIG. 2;

FIG. 4 shows a diagram of the components of the thermographic camera ofFIG. 1 in an embodiment of the present invention

FIG. 5 shows radiance curves related to blackbody radiation from anobject a different emissivities and illustrates a process by which atemperature of the object is determined at a superpixel from themeasurements obtained at pixels of the superpixel;

FIG. 6 shows a scanning electron micrograph of carbon nanotube (CNT)segments capable of measuring a radiance level using plasmonicinteractions for use in a pixel of the focal plane array;

FIG. 7 shows a spectral responsiveness of CNT sections toelectromagnetic radiation such as shown in FIG. 6, based on lengths ofthe CNT sections;

FIG. 8 shows a dynamically tunable pixel that can be used in a focalplane array of a thermographic camera in embodiments of the invention;

FIG. 9 shows an illustrative gate voltage that can be applied at thedynamically tunable pixel of a focal plane array and the resultingresonance frequency of a plasmonic material of the pixel correspondingto the gate voltage;

FIG. 10 shows a substrate of the focal plane array provided after aninitial fabrication stage of a plasmonic focal plane array according toembodiments of the invention;

FIG. 11 shows a fabrication stage of the focal plane array according toembodiments of the invention;

FIG. 12 shows a fabrication stage of the focal plane array according toembodiments of the invention;

FIG. 13 shows a fabrication stage of the focal plane array according toembodiments of the invention;

FIG. 14 shows a fabrication stage of the focal plane array according toembodiments of the invention; and

FIG. 15 shows a fabrication stage of the focal plane array according toembodiments of the invention.

DETAILED DESCRIPTION

Various embodiments of the invention are described herein with referenceto the related drawings. Alternative embodiments of the invention can bedevised without departing from the scope of this invention. Variousconnections and positional relationships (e.g., over, below, adjacent,etc.) are set forth between elements in the following description and inthe drawings. These connections and/or positional relationships, unlessspecified otherwise, can be direct or indirect, and the presentinvention is not intended to be limiting in this respect. Accordingly, acoupling of entities can refer to either a direct or an indirectcoupling, and a positional relationship between entities can be a director indirect positional relationship. Moreover, the various tasks andprocess steps described herein can be incorporated into a morecomprehensive procedure or process having additional steps orfunctionality not described in detail herein.

The following definitions and abbreviations are to be used for theinterpretation of the claims and the specification. As used herein, theterms “comprises,” “comprising,” “includes,” “including,” “has,”“having,” “contains” or “containing,” or any other variation thereof,are intended to cover a non-exclusive inclusion. For example, acomposition, a mixture, process, method, article, or apparatus thatcomprises a list of elements is not necessarily limited to only thoseelements but can include other elements not expressly listed or inherentto such composition, mixture, process, method, article, or apparatus.

Additionally, the term “exemplary” is used herein to mean “serving as anexample, instance or illustration.” Any embodiment or design describedherein as “exemplary” is not necessarily to be construed as preferred oradvantageous over other embodiments or designs. The terms “at least one”and “one or more” can be understood to include any integer numbergreater than or equal to one, i.e. one, two, three, four, etc. The terms“a plurality” can be understood to include any integer number greaterthan or equal to two, i.e. two, three, four, five, etc. The term“connection” can include both an indirect “connection” and a direct“connection.”

The terms “about,” “substantially,” “approximately,” and variationsthereof, are intended to include the degree of error associated withmeasurement of the particular quantity based upon the equipmentavailable at the time of filing the application. For example, “about”can include a range of ±8% or 5%, or 2% of a given value.

For the sake of brevity, conventional techniques related to making andusing aspects of the invention may or may not be described in detailherein. In particular, various aspects of computing systems and specificcomputer programs to implement the various technical features describedherein are well known. Accordingly, in the interest of brevity, manyconventional implementation details are only mentioned briefly herein orare omitted entirely without providing the well-known system and/orprocess details.

Turning now to an overview of technologies that are more specificallyrelevant to aspects of the invention, a thermographic camera produces animage of an object based on the temperature of the object. Objects canbe treated as blackbody radiators or “blackbodies” for thermographicimaging purposes. A blackbody is a perfectly opaque and non-reflectivematerial. The thermal emission from a blackbody is given by Planck'slaw, which specifies that the power per unit wavelength B_(λ)(λ,T) isgiven by:

$\begin{matrix}{{B_{\lambda}\left( {\lambda,T} \right)} = {\frac{2\; {hc}^{2}}{\lambda^{5}}\frac{1}{{\exp \left( \frac{hc}{\lambda \; k_{B}T} \right)} - 1}}} & \left( {{Eq}.\mspace{11mu} 1} \right)\end{matrix}$

where λ is the wavelength, h is Planck's constant, c is the speed oflight, T is the temperature of the object, and k_(B) is Boltzmann'sconstant. The curve drawn out by Planck's law peaks at a characteristicwavelength that is associated with a maximum temperature of theblackbody. Many objects however are not pure blackbodies and theiremission is only a fraction of the emission of a blackbody. Thisfraction is known as the emissivity, and is defined as:

ε=A _(λ)(λ,T)/B _(λ)(λ,T)   (Eq. 2),

where A_(λ)(λ,T) is the emission of the object, and B_(λ)(λ,T) is theemission of an ideal blackbody. Emissivities of materials can have abroad range of values from between an emissivity of 1 for a perfectabsorber and an emissivity of 0 for a perfect reflector. For example,aluminum foil has an emissivity of 0.03, whereas water is almost anideal black body, with an emissivity of 0.96. Due to the effect ofemissivity, when using a single-wavelength thermographic camera, objectswith different emissivities but identical temperatures can appearincorrectly on the camera to have different temperatures.

Embodiments of the present invention provides a thermal imaging deviceor thermographic camera for measuring both characteristic temperatureand emissivity of an object using multi-spectral measurements.Embodiments of the invention employ plasmonic materials in the thermalimaging device in order to detect radiance levels at variouswavelengths. Plasmonic materials include plasmonic absorbers whichinteract with electromagnetic fields to measure power levels at selectedwavelengths of the electromagnetic radiation via plasmonic interaction.Surface plasmons are charge oscillations in materials coupled to theoptical field or the electromagnetic field. Due to the strength ofplasmonic interactions, plasmonic materials can strongly absorb light,even when the plasmonic materials are nanostructures whose size issignificantly less than the free-space wavelength of light.Plasmon-resonance wavelengths correspond to peak absorption in amaterial as a function of optical wavelength. These plasmon resonancewavelengths are functions of the shape and/or size of the plasmonicmaterial.

The thermal imaging device according to embodiments of the invention caninclude an array of pixels generally grouped together in a superpixel.Each pixel includes a plasmonic absorber that is sensitive to of theelectromagnetic spectrum at an individual or characteristic wavelengthof the plasmonic absorber and thus can be used to measure the radiancefrom an object at the selected wavelength. With each pixel of asuperpixel responsive at its characteristic wavelength, a superpixel cangenerate radiance measurements for a plurality of wavelengths. Theseradiance measurements can be used to determine a radiance curve forelectromagnetic radiation received at the superpixel. The determinedradiance curve can be compared to a blackbody radiance curve having asame characteristic wavelength in order to determine an emissivity ofthe object and a temperature of the object. The temperature of theobject can be used to provide a thermal image, or thermal-basedelectronic image, of the object.

Referring now to FIG. 1, a thermographic camera system 100 is shown inembodiments of the present invention. The system 100 includes athermographic camera 102 that receives electromagnetic radiation 110emitted by an object 108. The electromagnetic radiation 110 includesthermal radiation such as radiation in an infrared region of theelectromagnetic spectrum, including the far infrared radiation region.The thermographic camera 102 generates electrical signals that areindicative of radiance levels at one or more wavelengths in response tothe electromagnetic radiation received from the object 108. Thethermographic camera 102 provides these electrical signals to aprocessor 104. The processor 104 calculates temperatures for each of theelectrical signals and assigns a color or other coding scheme for thedetermined temperatures. The color or coding scheme is provided to adisplay 106 in order to form a thermal image 112 of the object 108 atthe display 106. In various embodiments, the thermographic camera 102and the processor 104 can be provided as a single unit or device. Inother embodiments, the thermographic camera 102, processor 104 anddisplay 106 can be provided as in a single unit or device.

FIG. 2 shows a focal plane array 200 that is included in thethermographic camera 102 according to embodiments of the presentinvention in order to create a thermal image. The focal plane array 200is an optically-sensitive layer of plasmonic material and includes atwo-dimensional array of superpixels 202 which are used to obtain athermal profile of the object 108. In the exemplary embodiment, thefocal plane array 200 includes a 5×5 array of superpixels. However, itis to be understood that the focal plane array 200 is not limited tothis number of superpixels and that, in various embodiments, the numberof superpixels can number in the hundreds or thousands. An exemplarysuperpixel 202 has been circled for illustrative purposes and anexpanded view of the superpixel 202 is shown in FIG. 3.

Referring to FIG. 3, the illustrative superpixel 202 of FIG. 2 includesfour pixels, labelled A, B, C and D, that are arranged to form a square.The specific example of four pixels to a superpixel is not meant to be alimiting aspect of the invention and is shown for illustrative purposesonly. In various embodiments, a superpixel can include any number ofpixels. In addition, the shapes of the pixels and the superpixels, thegeometric arrangement of the pixels within a superpixel and thegeometric arrangement of the superpixels within the focal plane arraycan be any suitable shape and/or geometrical arrangement.

Each pixel (A, B, C, D) is sensitive to radiance levels at a particularwavelength of the electromagnetic spectrum. When a pixel (A, B, C, D)receives electromagnetic radiation at the wavelength (the “resonancewavelength”) at which the pixel is sensitive, the pixel generates asignal indicative of a radiance level for the received electromagneticradiation at the resonance wavelength, thereby providing a measurementof power at the resonance wavelength. In various embodiments, theresonance wavelength of each pixel (A, B, C, D) is different from theresonance wavelengths of the other pixels. In other words,λ_(A)≠λ_(B)≠λ_(C)≠λ_(D). Pixel A measures the radiance level R_(λA) at afirst wavelength λ_(A), pixel B measures the radiance level R_(λB) at asecond wavelength λ_(B), pixel C measures the radiance level R_(λC) at athird wavelength λ_(C), and pixel D measures the radiance level R_(λD)at a fourth wavelength λ_(D). The resonance wavelength of a pixel is aproduct of the materials and specifications of the pixel. Thesematerials and specifications can be selected during manufacture of thepixel.

FIG. 4 shows a diagram of the components of the thermographic camera 102of FIG. 1 in one embodiment of the present invention. The thermographiccamera 102 includes the focal plane array 200 of FIGS. 2 and 3. Thefocal plane array 200 is disposed at a focal plane of lens 402 whichdirects the electromagnetic radiation 110 from object 108 onto the focalplane array 200. The focal plane array 200 is disposed or locatedbetween a top contact layer 404 and a bottom contact layer 406. The topcontact layer provides an array of electrodes to a top side of the focalplane array 200, and the bottom contact layer 406 provides an array ofelectrodes to a bottom side of the focal plane array 200. The topcontact layer 404 can be made of a first metal while the bottom contactlayer 406 can be made of a second metal in order that the top contactlayer 404 and the bottom contact layer 406 have different workfunctions. In various embodiment, the first metal is palladium while thesecond metal is titanium.

Each pixel of the focal plane array 200 is coupled to an electrode ofthe top contact layer 404 and an electrode of the bottom contact layer406 in order to provide an electrical path between these electrodes. Theelectrodes connect the pixel to a sensor 410. In various embodiments,the sensor is a voltmeter. As the pixel receives electromagneticradiation directed onto it by lens 402, a potential difference iscreated between the top electrode and bottom electrode of the pixel. Thepotential difference is indicative of a radiance level of the receivedelectromagnetic radiation at the resonance wavelength of the pixel. Thevoltmeter measures this potential difference by generating an electricalsignal indicative of the potential difference and transmits theelectrical signal to the processor 104. For a selected superpixel, theprocessor 104 receives electrical signals from the plurality of pixelsof the superpixel, thereby receiving measurements of radiance levels ata plurality of wavelengths.

FIG. 5 illustrates a process by which a temperature of the object 108 isdetermined at a superpixel from the measurements obtained from pixels ofthe superpixel. Wavelength is shown along the abscissa and power isshown along the ordinate. The radiance measurements for a selectedsuperpixel are shown plotted against their corresponding wavelengths.The processor 104 constructs a curve that provides a best fit of theradiance measurements of the superpixel to an equation (or curve) ofPlanck's Law using regression analysis or other suitable curve-fittingmethod in order to obtain an emission curve A_(λ)(λ,T) 502representative of electromagnetic radiation at the superpixel. Theprocessor 104 then determines the characteristic wavelength λ_(ch) ofthe emission curve A_(λ)(λ,T) 502. The emission curve A_(λ)(λ,T) 502 forthe superpixel can be compared to a blackbody spectrum curve B_(λ)(λ, T)504 having the same characteristic wavelength in order to obtain anemissivity corresponding to the received radiation and a blackbodytemperature for the received radiation at the superpixel.

Repeating this process for each superpixel, the processor 104 thereforedetermines a blackbody temperature for each of the superpixels. Theprocessor 104 then assigns a color or other coding scheme to thedetermined blackbody temperatures and displays the color or codingscheme at display 106, thereby producing a thermal image of the object108 at the display 106.

Each pixel is able to interact with light at a selected wavelength ofthe electromagnetic spectrum using plasmonic materials or materialcomposed of plasmonic absorbers. Operation of these plasmonic absorbersis discussed below with respect to FIGS. 6-9. An exemplary plasmonicabsorber includes carbon nanotube sections or segments which arediscussed below with respect to FIGS. 6 and 7.

FIG. 6 shows a scanning electron micrograph of carbon nanotube (CNT)segments capable of measuring a radiance level using plasmonicinteractions. Carbon nanotubes include carbon atoms that are arranged toform a cylindrical structure, generally on a nanoscale. FIG. 6 shows afirst carbon nanotube in a top panel 602 and a second carbon nanotube ina bottom panel 604. The first carbon nanotube and the second carbonnanotube are each oriented so that their longitudinal axes extended inthe direction of arrow 610. Each carbon nanotube has been sectioned bycutting the carbon nanotube in a plane perpendicular to the longitudinalaxis, thereby creating CNT sections 602 a, . . . , 602 n from the firstcarbon nanotube (shown as dark bands in top panel 602 and having lengthL₁) and creating CNT sections 604 a, . . . 604 n from the second carbonnanotube (shown as dark bands in bottom panel 604 and having length L₂).These CNT sections can be in the form of ring.

A selected CNT section (e.g., CNT section 602 a) is a plasmonic absorberand acts as a resonant cavity that serves to localize plasmons, with theends of the CNT section functioning as plasmon reflectors. A plasmonresonance corresponds to a longitudinal charge oscillation that occursbetween the ends of the CNT section. The resonance wavelength of the CNTsection is proportional to the length of the CNT section. Therefore, CNTsection 602 a with length Li has different resonance wavelength that CNTsection 604A with length L₂. Since L₁<L₂ the resonance wavelength of CNTsection 602 a is less than the resonance wavelength of CNT section 604a. The resonance wavelength can also be tuned by changing such factorsas the thickness of a film of the CNTs and the doping level of the CNTs.The CNT sections can be used to create a pixel of the focal plane array200 that is sensitive to electromagnetic radiation at a specifiedwavelength.

FIG. 7 shows a spectral responsiveness of CNT sections toelectromagnetic radiation based on lengths of the CNT sections.Wavenumber in 10³ cm⁻¹ is shown along the abscissa and attenuation (%)is shown along the ordinate. The length of the CNT section indicates theresonance wavelength of the CNT, with resonance frequency and wavenumberbeing inversely proportional to the resonance wavelength. Thus a CNTsection having length 160 nanometers (nms) has a peak absorptioncentered at a wavenumber of about 3800 cm⁻¹, a CNT section having length260 nanometers (nms) has a peak absorption centered at a wavenumber ofabout 3000 cm⁻¹, and a CNT section having length 480 nanometers (nms)has a peak absorption centered a wavenumber of about 2400 cm⁻¹.

In alternate embodiments, other plasmonic materials, such as graphenenanoribbons or metal nanoparticles can be used in addition to or inplace of CNT sections. The resonance wavelengths of these plasmonicmaterials can be tuned based on the geometry of the graphene nanoribbonsor metal nanoparticles. The tunability of plasmonic materials can beused to make devices that allow plasmon resonances over a broad range ofwavelengths. For instance, the plasmon resonances of carbon nanotubesand graphene nanoribbons can both span the mid-infrared throughterahertz range, which is a suitable wavelength for thermographiccameras.

In various embodiments, the plasmonic absorber converts plasmonicinteractions into electrical signals using at least one of thephotothermoelectric effect, hot-electron tunneling, or a bolometriceffect.

In the photothermoelectric effect, the plasmonic absorber is contactedon either side by metals. The two metals are of different materials andtherefore have different work functions. In an exemplary embodiment, onemetal is palladium and another metal is titanium. In this method, theplasmons absorb the incoming electromagnetic radiation, thereby heatingthe plasmonic material. The resulting temperature difference between theplasmonic material and the metal contacts creates an electrical voltagevia the Seebeck effect. Because the two contact metals are different,the voltage of the two different contacts will be different, giving riseto a net voltage across the pixel. This voltage is recorded at thesensors and is then processed by the processor 104 to determine a powerof the electromagnetic radiation.

In hot-electron tunneling, the plasmonic absorber is contacted by twodifferent metals, similar to in the photothermoelectric effect. However,once the plasmons absorb the infrared radiation, and before the plasmonsrelax into thermal energy, the charges of the plasmonic absorber tunnelinto the metal contacts, thereby producing an electrical current andvoltage. The response time for hot-electron tunneling can be faster thanthe response time for the photothermoelectric effect. While for eitherof these processes (photothermoelectric effect and hot-electrontunneling) the pixel is the same, the process that ends up dominatingwill depend on the relaxation time of charges in the plasmonic absorber,and the characteristics of the electrical contacts to the plasmonicabsorber.

In bolometry, a voltage is applied across the plasmonic absorber, andits conductance is measured. The conductance of the plasmonic absorberchanges as a result of the heat created by the plasmonic absorption ofthe electromagnetic radiation. This change in conductance is measured bythe voltmeter.

FIG. 8 shows a dynamically tunable pixel 800 that can be used in a focalplane array 200 of a thermographic camera 102 in another embodiment ofthe invention. The dynamically tunable pixel 800 includes a plasmonicmaterial 802 sandwiched between a top contact 804 and bottom contact806. The top contact 804 and bottom contact 806 are coupled to oppositeends of the plasmonic material and are further coupled to a voltagesource 808 that applies a gate voltage across the plasmonic material802. Since many plasmonic materials, such as graphene, carbon nanotubes,and GaAs, are semiconductors, the voltage can be treated as a gatevoltage of a transistor, which dynamically tunes or selects theresonance wavelength of the plasmonic material 802 by the level of gatevoltage.

FIG. 9 shows an illustrative gate voltage that can be applied at thedynamically tunable pixel 800 and the resulting resonance frequency ofthe plasmonic material of the pixel corresponding to the gate voltage.The resonance frequency and resonance wavelength change with gatevoltage in a controllable manner, allowing several radiance measurementsto be obtained over a definable time interval at a single pixel.Therefore the gate voltage can be used to select a first resonancewavelength of the plasmonic material so that a radiance measurement canbe obtained at the first resonance wavelength. The gate voltage can thenbe adjusted to select a second resonance wavelength of the plasmonicmaterial so that a radiance measurement can be obtained at the secondresonance wavelength.

Using dynamically tunable pixels, a superpixel need not have a pluralityof pixels, and can instead having a single pixel that is swept over arange of sensitive wavelengths over a period of time. Measurements usingthis single pixel can be used to independently determine both ε and Tusing Eqs. (1) and (2) as well as the process illustrated in FIG. 5.

FIGS. 10-15 illustrate a fabrication process for the plasmonic focalplane array used in thermographic cameras for thermal imaging. For thesake of brevity, conventional techniques related to fabrication of focalplane arrays may or may not be described in detail herein. Moreover, thevarious tasks and process steps described herein can be incorporatedinto a more comprehensive procedure or process having additional stepsor functionality not described in detail herein. In particular, varioussteps in the fabrication of focal plane arrays are well known and so, inthe interest of brevity, many conventional steps will only be mentionedbriefly herein or will be omitted entirely without providing thewell-known process details.

Additionally, spatially relative terms, e.g., “beneath,” “below,”“lower,” “above,” “upper,” and the like, are used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. It will beunderstood that the spatially relative terms are intended to encompassdifferent orientations of the device in use or operation in addition tothe orientation depicted in the figures. For example, if the device inthe figures is turned over, elements described as “below” or “beneath”other elements or features would then be oriented “above” the otherelements or features. Thus, the term “below” can encompass both anorientation of above and below. The device can be otherwise oriented(e.g., rotated 90 degrees or at other orientations), and the spatiallyrelative descriptors used herein should be interpreted accordingly.

FIG. 10 shows a substrate 1002 of the focal plane array provided in afabrication stage 1000. FIG. 11 shows a stage 1100 in which the bottommetal layer 1102 is formed on top of the substrate 1002 by a suitabledeposition method and a layer of plasmonic material 1104 is formed ontop of and in direct contact with the bottom metal layer 1102. FIG. 12shows a fabrication stage 1200 in which an etching mask 1204 is providedover the plasmonic material 1104. FIG. 13 shows a fabrication stage 1300in which the plasmonic material 1104 is etching using a suitablelithography or etching process, such as reactive ion etching, forexample. As part of this patterning process, multiple shapes ofplasmonic particles or pixels can be created. FIG. 14 shows afabrication stage 1400 in which the etch mask has been removed, leavingan array of pixels sensitive to a selected wavelength. FIG. 15 shows afabrication stage 1500 in which the top metal contact 1502 is depositedon top of and in direct contact with the pixels in order to provide anelectrical circuit from a bottom layer through to the top layer via thepixels. In various embodiments, the process of depositing plasmonicmaterial and etching the plasmonic material can be repeated forplasmonic materials of difference resonance wavelengths in order toprovide pixels having different resonance wavelengths.

Plasmonic materials can be grown or deposited, and can need to bepatterned so as to properly tune their resonant frequencies. Severalexemplary plasmonic materials can include silicon, GaAs, TiN, carbonnanotubes, graphene, other two dimensional metals, and bulk metals thathave a low charge density.

Because the thermographic camera in embodiments of the present inventionhas pixels with different wavelength sensitivity, the thermographiccamera can be used any selected wavelength regime, including midinfrared, far infrared, etc. This allows the thermographic camera to beused with very hot objects (e.g. missiles) typically have peak emissionin the mid infrared and/or objects near room temperature have peakinfrared in the far infrared.

The present invention may be a system, a method, and/or a computerprogram product. The computer program product may include a computerreadable storage medium (or media) having computer readable programinstructions thereon for causing a processor to carry out aspects of thepresent invention.

The computer readable storage medium can be a tangible device that canretain and store instructions for use by an instruction executiondevice. The computer readable storage medium may be, for example, but isnot limited to, an electronic storage device, a magnetic storage device,an optical storage device, an electromagnetic storage device, asemiconductor storage device, or any suitable combination of theforegoing. A non-exhaustive list of more specific examples of thecomputer readable storage medium includes the following: a portablecomputer diskette, a hard disk, a random access memory (RAM), aread-only memory (ROM), an erasable programmable read-only memory (EPROMor Flash memory), a static random access memory (SRAM), a portablecompact disc read-only memory (CD-ROM), a digital versatile disk (DVD),a memory stick, a floppy disk, a mechanically encoded device such aspunch-cards or raised structures in a groove having instructionsrecorded thereon, and any suitable combination of the foregoing. Acomputer readable storage medium, as used herein, is not to be construedas being transitory signals per se, such as radio waves or other freelypropagating electromagnetic waves, electromagnetic waves propagatingthrough a waveguide or other transmission media (e.g., light pulsespassing through a fiber-optic cable), or electrical signals transmittedthrough a wire.

Computer readable program instructions described herein can bedownloaded to respective computing/processing devices from a computerreadable storage medium or to an external computer or external storagedevice via a network, for example, the Internet, a local area network, awide area network and/or a wireless network. The network may comprisecopper transmission cables, optical transmission fibers, wirelesstransmission, routers, firewalls, switches, gateway computers and/oredge servers. A network adapter card or network interface in eachcomputing/processing device receives computer readable programinstructions from the network and forwards the computer readable programinstructions for storage in a computer readable storage medium withinthe respective computing/processing device.

Computer readable program instructions for carrying out operations ofthe present invention may be assembler instructions,instruction-set-architecture (ISA) instructions, machine instructions,machine dependent instructions, microcode, firmware instructions,state-setting data, or either source code or object code written in anycombination of one or more programming languages, including an objectoriented programming language such as Smalltalk, C++ or the like, andconventional procedural programming languages, such as the “C”programming language or similar programming languages. The computerreadable program instructions may execute entirely on the user'scomputer, partly on the user's computer, as a stand-alone softwarepackage, partly on the user's computer and partly on a remote computeror entirely on the remote computer or server. In the latter scenario,the remote computer may be connected to the user's computer through anytype of network, including a local area network (LAN) or a wide areanetwork (WAN), or the connection may be made to an external computer(for example, through the Internet using an Internet Service Provider).In some embodiments, electronic circuitry including, for example,programmable logic circuitry, field-programmable gate arrays (FPGA), orprogrammable logic arrays (PLA) may execute the computer readableprogram instructions by utilizing state information of the computerreadable program instructions to personalize the electronic circuitry,in order to perform aspects of the present invention.

Aspects of the present invention are described herein with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems), and computer program products according to embodiments of thepresent invention. It will be understood that each block of theflowchart illustrations and/or block diagrams, and combinations ofblocks in the flowchart illustrations and/or block diagrams, can beimplemented by computer readable program instructions.

These computer readable program instructions may be provided to aprocessor of a general purpose computer, special purpose computer, orother programmable data processing apparatus to produce a machine, suchthat the instructions, which execute via the processor of the computeror other programmable data processing apparatus, create means forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks. These computer readable program instructionsmay also be stored in a computer readable storage medium that can directa computer, a programmable data processing apparatus, and/or otherdevices to function in a particular manner, such that the computerreadable storage medium having instructions stored therein comprises anarticle of manufacture including instructions which implement aspects ofthe function/act specified in the flowchart and/or block diagram blockor blocks.

The computer readable program instructions may also be loaded onto acomputer, other programmable data processing apparatus, or other deviceto cause a series of operational steps to be performed on the computer,other programmable apparatus or other device to produce a computerimplemented process, such that the instructions which execute on thecomputer, other programmable apparatus, or other device implement thefunctions/acts specified in the flowchart and/or block diagram block orblocks.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods, and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof instructions, which comprises one or more executable instructions forimplementing the specified logical function(s). In some alternativeimplementations, the functions noted in the block may occur out of theorder noted in the figures. For example, two blocks shown in successionmay, in fact, be executed substantially concurrently, or the blocks maysometimes be executed in the reverse order, depending upon thefunctionality involved. It will also be noted that each block of theblock diagrams and/or flowchart illustration, and combinations of blocksin the block diagrams and/or flowchart illustration, can be implementedby special purpose hardware-based systems that perform the specifiedfunctions or acts or carry out combinations of special purpose hardwareand computer instructions.

What is claimed is:
 1. A thermal imaging device, comprising: anoptically-sensitive layer including a superpixel having at least onepixel, the at least one pixel including a plasmonic absorber configuredto obtain radiance measurements of electromagnetic radiation emittedfrom an object at a plurality of wavelengths; and a processor configuredto determine an emissivity and temperature for the electromagneticradiation received at the plasmonic material from the object using theradiance measurements and to form an image of the object from thedetermined emissivity and temperature.
 2. The thermal imaging device ofclaim 1 further comprising a sensor coupled to the plasmonic absorberfor measuring a voltage across the plasmonic absorber generated inresponse to the electromagnetic radiation.
 3. The thermal imaging deviceof claim 1, wherein the at least one pixel includes plasmonic absorberdynamically tunable to at least two resonance wavelengths via an appliedvoltage, wherein radiance measurements are obtained at the plasmonicabsorber at each of the at least two resonance wavelengths.
 4. Thethermal imaging device of claim 1, wherein the at least one pixelincludes a first pixel configured to measure radiance at a firstresonance wavelength and a second pixel configured to measure radianceat second resonance wavelength.
 5. The thermal imaging device of claim1, wherein the plasmonic absorber further comprises a carbon nanotubesegment having a resonance wavelength related to a length of the carbonnanotube segment.